HIV infection is frequently characterized by neurocognitive deficits collectively labeled as HIV-associated neurocognitive disorders (HAND). While the use of combination antiretroviral therapies (CART) have dramatically reduced AIDS-related morbidity, HAND remains a significant public health concern linked to impaired everyday functioning and poor quality of life in HIV-positive (HIV+) individuals. Despite the continued prevalence of HAND in the CART era, there are no empirically validated strategies to effectively treat neurocognitive dysfunction in this population. Physical activity (PA) has been utilized as an effective non- pharmacological method to improve cognitive performance in individuals with dementia and psychiatric disorders. PA interventions in HIV+ subjects are reported to improve cardiopulmonary fitness, but the effects of PA on HAND have not been well characterized. Previous HIV PA interventions also involve rigorous PA (running on a treadmill) and significant participant resources (traveling to a gym multiple times per week) that may not be suitable or practical for many HIV+ individuals. We propose to conduct a randomized controlled trial to administer a personalized interactive mobile phone text messaging intervention to increase moderate PA and improve cognitive function in HIV+ participants with HAND. This study will utilize a Short Message Service/Multimedia Message Service (SMS/MMS) platform developed by the California Institute for Telecommunications and Information Technology (Calit2), which conducts state-of-art health promotions using mobile electronic devices. 50 HIV+ participants will be randomly assigned to a control group or a 4-month intervention group that will receive daily SMS/MMS mobile phone messages designed to increase PA. The intervention condition, based on control theory, is structured to promote goal-setting by using SMS text prompts and MMS images to monitor PA, provide goal reminders, promote goal strategies, and deliver feedback on goal progress. We will conduct focus groups to identify HIV-specific PA limitations (e.g., medication side effects, neuropathy) and identify ways to overcome these barriers. Text messages will be tailored to each individual, including their social contacts and environment. We hypothesize that HIV+ participants administered this intervention will exhibit a significant increase in PA compared to a control group as assessed by pedometer step counts, accelerometer activity, and self-reported PA on the 7-Day Physical Activity Recall (PAR). Further, we propose that the intervention will improve cognitive performance and everyday functioning compared to the control condition as quantified by a comprehensive neuropsychological battery and self-report and performance-based measures of daily living activities. Findings from this proposal will lay the groundwork for development of novel large-scale personalized mobile PA interventions dedicated to treating HAND and improving the quality of life for HIV+ individuals.